Antirolling and antipitching supporting method and device for a tank during transportation

ABSTRACT

An antirolling and antipitching device for a ship-borne spherical tank movably suspended from the ship&#39;&#39;s hull and comprising at least one horizontal ring surrounding said tank and freely interposed between the latter and said hull, said ring being formed with radial guide elements engaging in vertically and radially horizontally sliding relationship corresponding slide means secured to said tank and to said hull, respectively.

[451 Dec. 10, 1974 United States Patent Alleaume I 114/74 A Bridges 114/74 A X Alleaume..........................

3,276,412 10/1966 SUPPORTING METHOD AND DEVICE FOR 3,425,583 2/ 3 A TANK DURING TRANSPORTATION 3583'352 6/19 1 [75] Inventor:

[ ANTIROLLING AND ANTIPITCHING Jean Alleaume, Saint-Cloud, France Assignee: Technigaz, Paris, France Primary Examiner-William H. Schultz Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin Appl. No.: 303,012

ABSTRACT [30] Foreign Application Priority Data June 6, 1972 France........................ 72.20337 78 Glm BS ma 0 b n w ,wB A on" O U 2 u 2 m 5 m 1 u H 0 U 2 a 2 U C G S L U m l 2 1 5 5 .l l

[58] Field of Search 114/74 A; 220/15, 9 A, 220/9 LG, 69; 248/317 [56] References Cited UNITED STATES PATENTS 3,071,094 1/1963 Leroux......I....................... 220/15 X 16 Claims, 4 Drawing Figures PATENTEL DEC 1 0 i974 SHEET 2 OF 2 ANTIROLLING AND ANTIPITCHING SUPPORTING METHOD AND DEVICE FOR A TANK DURING TRANSPORTATION The present invention relates generally to and has essentially for its object various improvements in and modifications of the device described in the U.S. Pat. No. 3,712,257 and, more particularly but not exclusively, a particular form of embodiment of the latter.

The aforementioned prior U.S. patent relates to an antirolling and antipitching supporting device, in particular an auxiliary device, for a transported rigid tank, preferably having a shape of revolution at least about a geometrical axis which is substantially vertical with respect to the carrying vehicle and suspended movably from the latter by means of a system of main supports. Such a device comprises at least one system of spaced stationary bearing members distributed about the periphery of the said tank while at the same time being at least approximately in at least one and the same relative horizontal plane and each of which is substantially rigid or practically not deformable at least in a horizontal direction perpendicular to the straight line locally normal to the said tank passing through the bearing member considered, while at the same time being connected to the said tank in such a manner that the latter is immobilized locally in the said direction but is freely movable in at least the relative vertical, substantially normal meridian plane passing through the said bearing member. In this known device, each stationary bearing member is constituted by a rolling or sliding guiding element such as for instance a sliding or rolling pad solid with an external stationary structure surrounding the tank and co-operating through sliding or rolling contact with an at least approximately radial forced-guiding bearing forming for instance a slide-way or bilateral rolling track externally solid with the tank. During the rolling and/or pitching motions imparted to the tank, each said stationary bearing member applies, by way of a bearing reaction against its associated forced-guiding bearing solid with the tank, a force which is tangential to the said tank at a point spaced radially outwardly from the tank wall, thus producing, in the tank wall, a bending moment and, therefore, a corresponding bending stress increasing in proportion to the increase in the length of the lever arm represented by the distance from the point of application of the said force to the wall of the tank. Now the length of this lever arm is variable owing to the relative thermal deformations of the tank and the external stationary carrying structure surrounding it, respectively, which cause relative displacement in mutually opposite directions, i.e. motions towards or away from one another, of two mutually adjacent physical points pertaining to the tank and the surrounding structure respectively. Thus and in particular, under the action of a contraction of these constructions, caused in particular by the pre-cooling of the tank with a view of storing of liquefied natural gas at a very low temperature, such as methane, the cooperating forced-guiding means, such as each pad pertaining to the external stationary structure and its associated forced-guiding bearing pertaining to the tank, tend to move away from one another, thus causing an increase in the length of the said lever arm and, therefore, of the bending moment acting upon the skin of the tank, this being detrimental to a good behaviour of the wall of the latter, since it is accompanied by a risk of cracking or like failure of the tank wall, and this is a se rious drawback.

The invention has mainly for its object to remove this drawback by creating a device enabling the length of each said lever arm to be maintained substantially constant and preferably at a minimum value. To this end, the present invention provides an antirolling and antipitching supporting device, in particular an auxiliary device, for a transported rigid tank, preferably having a shape of revolution about at least a geometrical axis which is substantially vertical with respect to the carrying vehicle and is movably suspended from the latter by means of a system of main supports, the said device being of the aforementioned type comprising at least one system of spaced stationary bearing members distributed about the periphery of the said tank while at the same time being approximately in at least one and the same relative horizontal plane and each of which is substantially rigid or practically not deformable at least in a horizontal direction perpendicular to the local normal to the said tank passing through the bearing member considered, while at the same time being connected to the said tank in such a manner that the latter is 10- cally immobilized in the said direction but freely movable in at least the relative vertical, substantially normal meridian plane passing through the said bearing member. In order to solve the aforementioned technical problem, the device according to the present invention is characterized in that it comprises a substantially horizontal intercalated ring coaxially surrounding the said tank while at the same time being freely interposed, with clearance, between the latter and the plurality of peripherally arranged stationary bearing members as well as mutually co-operating forced-guiding means placed on either, respectively radially internal and external side of the said ring between the latter, on the one hand, and the said tank and the said stationary bearing members, on the other hand, while at the same time being solid with respectively the said ring, the said tank and the said stationary bearing members, so as to constitute, between the said ring, on the one hand, and the tank and the stationary bearing members, on the other hand, a link which is variable only to allow a free thermal contraction or expansion of the said ring and its mobility in a relative vertical or axial direction.

Owing to this arrangement, any possible variations of the said lever arms, caused by the variations in temperature, especially increases in the length of the said lever arms caused by temperature decreases or coolings, are reduced to a minimum or to zero, so that the effects of the corresponding secondary bending moments on the tank, in particular owing to the contraction of the latter during its pre-cooling, are thus effectively compensated for by a reduction of their increase to a minimum value or to zero. This advantageous action is obtained owing to the presence of the said ring which is substantially free from any thermal stress owing to its free thermal deformation, so that the thermal deformations of the ring substantially follow the thermal deformations of the tank. Thus, when the tank contracts under the action of its being cooled, the said ring, which is in thermal connection or contact with the tank, is subjected to a substantially similar cooling and, therefore, contracts, thus producing a radial displacement of its various points inwardly at least approximately equal to the radial displacement of the external surface of the tank wall inwardly.

According to another feature of the invention, the said ring is provided, on its respectively radially internal and external peripheries, with circumferentially spaced and radially projecting guiding elements solid with one another, each external guiding element cooperating through bilateral sliding or rolling contact with a corresponding and mating external forcedguiding bearing formed by a said associated stationary bearing member, whereas each internal guiding element co-operates through bilateral sliding or rolling contact with an associated and mating internal forcedguiding bearing which is externally solid with the wall of the said tank, each pair of said co-operating guiding means, constituted by a guiding element and its associated forced-guiding bearing, being placed in the said corresponding relative vertical or meridian plane and allowing of a local relative motion in this plane.

According to still another feature of the invention, the said ring is supported unilaterally so as to balance its weight in order to preserve its relative mobility, on the one hand, in its horizontal plane and, on the other hand, in the relative vertical, at least ascending direction. This is obtained owing to the fact that, according to still another feature of the invention, the said ring is freely laid on several stationary and circumferentially spaced simple bearing supports or brackets. Alternatively and according to still another feature of the invention, the same effect is obtained when the said ring is suspended by means of supple or flexible connecting means such as cables or chains. According to still another feature of the invention, in each internal or external pair of said co-operating guiding means, constituted respectively by a guiding bearing and an associated guiding element, one of them is constituted by a clevis or yoke forming a female slide-way or guiding path and the other by a male guiding bracket or like dog member with sliding pads or rolling rolls or balls, constantly engaging the said slide-way.

The device according to the invention is therefore advantageous by its structurally simple construction, hence by its economical manufacture and mounting, as well as by its efficient and safe, hence highly reliable, operation.

The invention will be better understood and other objects, characteristics and advantages thereof will appear as the following description proceeds, with reference to the appended drawings given solely by way of example illustrating one form of embodiment of the invention and wherein:

FIG. 1 is a half cross-sectional view of a ship transporting one or several spherical tanks, only one of which is shown and equipped with a device according to the invention, the system of vertical suspension supports of the tank having been omitted;

FIG. 2 is a fragmentary perspective view, partially broken away and on a larger scale, of the encircled detail II of FIG. 1;

FIG. 3 is a fragmentary sectional top view, taken upon the line III-III of FIG. 4, illustrating the system shown in FIG. 2; and

FIG. 4 is a cross-sectional view taken upon the line IV-IV of FIG. 3.

According to the form of embodiment illustrated in FIG. 1, the aforesaid transport vehicle is constituted by a ship the double hull of which is designated generally by the reference numeral 101 and is provided, at its upper portion, with a main deck 102. In the hold 103 of the ship are mounted one or several tanks, for instance spherical tanks, 104, the upper portion of each of which, passing through the corresponding hatch 105, projects beyond the main deck 102. The tank 104 may also be circular cylindrical, for instance with a vertical axis, or it may have any other shape of revolution at least about a vertical axis. In the example illustrated, the centre 106 of each tank 104 is advantageously located in the medial longitudinal vertical plane 107 of the ship, although this is not necessarily so. The tank is for instance intended to contain a gas, in particular a liquefied natural gas at a very low temperature such as methane. In this case, the tank 104 as well as all its support and suspension members to which it is connected are advantageously made from a noble metal capable of withstanding low temperatures, such as for instance stainless steel or an equivalent metal, and the internal walls 108 of the hold 103 are advantageously coated, on their internal exposed surface facing the tank, with a layer of appropriate heat-insulating material (not shown), and the free space of the hold 103, between the internal walls 108 and the tank 104, may besides be filled with a suitable heat-insulating material.

The vertical suspension system of the tank is of the type mentioned in the aforementioned prior U.S. patent and, therefore, will not be described.

In the present case of a spherical or spheroidal tank admitting a relative horizontal plane, or equatorial plane, of symmetry, there are advantageously provided two systems of anti-rolling and antipitching bearing members, namely a lower system 109 and an upper system 110, respectively placed respectively at two superposed levels which are vertically symmetrical or equidistant with respect to the horizontal plane or equatorial plane 111 of the tank, the upper system being preferably substantially at the level of the main deck 102 of the ship. Referring to FIGS. 2 and 3, it is seen that each of said antirolling and antipitching systems 109, 110 comprises a plurality of stationary bearing members 112 located substantially in one and the same relative horizontal plane while at the same time being circumferentially spaced and distributed all around the tank 104 in the hold 103. Each bracket 112 is solid with the internal wall of the hold or of the corresponding hull structure 108 and is, for instance, welded to the latter. In order to reinforce the system of stationary bearing members 112, there are provided stiffening horizontal sheet-metal plates forming gussets 113 welded respectively between the successive stationary bearing members so as to connect the latter with one another and also to the wall 108 of the hull. Each bearing member 112 is advantageously in the shape of a clevis or yoke, the two spaced, substantially parallel arms of which are constituted respectively by brackets, the radially internal ends of which are provided, on their mutually opposite vertical surfaces, with a lining of heat-insulating material 114, each of which is constituted for instance by a block of compressed wood or the like maintained in a channel-like element such as solid with the corresponding arm of the clevis 112, each block 114 projecting inwardly beyond its fastening element 1 15. Each insulating block 1 14 may advantageously constitute, at the same time, a lining having antiwear properties with respect to sliding friction, so that the two mutually opposite linings form together a kind of guiding slide extending horizontally, or possibly vertically as well, and the mutually opposite bearing To each stationary bearing member 112 advanta- I geously corresponds a bearing or guiding element 116 extending at least approximately radially and outwardly and solid with, for instance welded to the tank 104 while at the same time projecting beyond the latter. Each guiding element 116 is advantageously constituted by a bracket, the external lateral faces of which are substantially parallel and vertical. Each guiding element 116 is preferably substantially symmetrical with respect to the meridian relative vertical plane passing through the axis of the corresponding bearing member 112.

At each level 109, 110 a circular ring 117 is interposed between the plurality of circumferentially arranged stationary bearing members 112 and the tank 104. The said ring is advantageously toroidal shape with a circular cross-section, but may also have any different shape, for instance a rectangular, square, oval or other shape. For the sake of weight saving, the ring 117 may be tubular or hollow. Opposite to each stationary bearing member 112, the ring 117 is provided with a projecting guiding element 118 which is solid, for instance welded, to the external periphery of the ring 117 and extends outwardly in a substantially radial direction. Each guiding element 118 is substantially in the form of a key-like bracket, the distance between the parallel, spaced and substantially vertical lateral wall surfaces of which corresponds substantially to the distance between the mutually opposite vertical parallel lateral faces of the blocks 114 of the corresponding stationary bearing member 112. Each guiding element 118 is preferably substantially symmetrical with respect to the meridian vertical plane of symmetry of the associated stationary bearing member 112 and penetrates between the blocks 114 with a sliding fit and in sliding contact with the latter. On its internal periphery the ring 117 is provided, opposite to each guiding element 116 solid with the tank, with a guiding clevis or yoke 119, the two arms of which are arranged symmetrically with respect to the relative vertical meridian plane of symmetry of the stationary bearing member 112. Each guiding clevis 119 thus projects radially inwards from the ring 117 and comprises two parallel and substantially vertical, mutually opposite bearing surfaces. the spacing of which corresponds substantially to the width of the associated guiding element 116 which thus penetrates with a sliding fit into the clevis 119. Each clevis 119 is for instance welded to the ring 117. The radial lengths of the bearing surface portions of each clevis 119 and of the associated guiding element 116 which are mutually in contact, are sufficient for the portions to remain constantly in contact with each other during the respective thermal deformations by contraction or expansion of the ring 117 and the tank 104, so that each guiding element 116 solid with the tank remains all the time engaged with its corresponding guiding clevis 119 solid with the ring 117. Likewise, the radial length of each external guiding element 118 solid with the ring is sufficient to keep it constantly engaged with the associated stationary bearing member 112 during the thermal deformations of the ring 117. The respective arrangements provided for the guiding means existing, on the one hand, between the ring 117 and the stationary structure 108 and, on the other hand, between the ring 117 and the tank 104, may of course be reversed. Thus, in each pair of external guiding means, formed by the co-operating elements 112 and 118, the main guiding element 118 may be secured to the stationary structure 108, the female guiding slide 1 12 then being secured to the ring 117. Likewise, the arrangement of each pair of internal guiding means, formed by I the elements 116 and 119, may be reversed, the female guiding clevis 119 being carried by the tank 104 and the main guiding element 116 being secured to the ring 117. Alternate arrangements may also be provided in which only some of the elements 118 are located on the ring 117 and some others on the stationary wall 108, whereas some of the elements 112 are located on the stationary wall 108 and some others on the ring 117, the same possibilities existing for the relative arrangements of the pairs of elements 116 and 119.

In the example illustrated, to each pair of external guiding means 112, 118 corresponds a pair of internal guiding means 116, 119, so that the number of pairs of internal guiding means is equal to the number of pairs of external guiding means. The number of pairs of internal guiding means 116, 119 may however be different from the number of pairs of external guiding means 112, 118 (it may for instance be greater or smaller than the latter). in this case, the pairs of internal guiding means are not necessarily radially aligned with the pairs of external guiding means, but respectively shifted angularly with respect to the latter.

By way of example, for a spherical tank with a diameter of 37.5 m, there are provided 110 pairs of external guiding means and the same number of pairs of internal guiding means distributed uniformly about the periph cry of the tank.

Each ring 117 is supported vertically by a number of stationary projecting brackets or the like supported seats (see P16. 4) secured on the structure of the external stationary wall 108 and projecting radially inwards. The number of carrying brackets 120 may be considerably smaller than that of the stationary bearing members 112 and, for the aforementioned specific tank, may be for example equal to 15 distributed uniformly about the latter. Each bracket 120 is advantageously arranged in the vertical plane of symmetry of a stationary bearing member 112 and the ring 117 is supported by the brackets 120 and freely bears upon the latter, for instance through the medium of its external projecting guiding elements 118. The insulating linking blocks 114, which may also form an antifriction lining for sliding contact therewith, instead of being interposed between the external guiding means 112, 118, may be provided between the internal guiding means 116, 119. In the case of the example illustrated, where the heatJnsulating linings 114 are provided between the external guiding means 112, 118, the tank 104 and ring 117, as well as the internal guiding means 1 16, 119 and the external guiding elements 118, are made from a noble metal withstanding low temperatures, such as stainless steel or steel alloyed with 9 nickel, whereas the external structure, formed in particular by the elements 108, 112, 113, may be made from ordinary structural steel.

Of course, the invention is by no means limited to the form of embodiment described and illustrated, which has been given by way of example only. In particular, it comprises all the means constituting technical equivalents to the means described as well as their combinations, should the latter be carried out according to the gist of the invention.

What I claim is:

1. In a construction including: a self-supporting structure undergoing roll and pitch rocking motions about two structure-bound orthogonal geometrical axes of swing, respectively; a rigid tank supported mainly in weight-bearing relationship and at least partially encompassed by said structure; and an auxiliary device for bodily constraining said tank against roll and pitch with respect to said structure while allowing substantially free thermal expansion and contraction thereof; the improvement consisting in that said device comprises: at least one ring externally surrounding said tank and interposed in spaced relationship between the later and said structure; said ring being substantially parallel to the plane defined by the respective directions of said axes of swing; movably co-operating discrete keying means integral with said ring, structure and tank, re-

spectively and providing slidable engagement of said ring with said structure and tank, respectively, to hold said ring against body motion parallel to said plane at least relative to said structure while allowing substantially free thermal expansion and contraction of said ring as well as substantially free body displacements thereof in parallel relation perpendicular to said plane; and weight-bearing means for unilaterally supporting said ring against its own weight while allowing its thermal expansion and contraction and body displacements therefrom.

2. An arrangement according to claim 1, wherein said keying means comprise: at least one external plurality of discrete keying devices distributed about the outer periphery of said ring between the latter and said structure at least approximately on a same horizontal level and consisting each one of a pair of mating ringbound and structure-bound members carried by said ring and structure, respectively, and co-operating in slidable forced-guiding relationship, said ring-bound member defining one of a key and key-way whereas said structure-bound member defines the other of a key and key-way and engages said corresponding ringbound member in slidable interfitting relationship; and at least one internal plurality of discrete keying devices distributed along the inner periphery of said ring and about the outer periphery of said tank between said ring and tank at least approximately on a same relative horizontal level and consisting each one of a pair of mating ring-bound and tank-bound elements carried by said ring and tank, respectively, and co-operating in slidable forced-guiding relationship, said ring-bound element defining one of a key and key-way whereas said tank-bound element defines the other ofa key and key-way and engages said associated ring-bound element in slidable interfitting relationship, each keying device being at least approximately symmetrical with respect'to a relative vertical center plane locally normal to the wall surface of said tank and perpendicular to said plane defined by said axes of swing; whereby the relative displacements of said ring and tank are confined to said relative vertical center planes.

3. An arrangement according to claim 2, wherein the general configuration of the contour of said ring conforms in at least approximately parallel relationship to the local shape of at least the adjacent portion of the outer wall surface of said tank whereby the thermal deformations of said ring at least approximately follow those of said adjacent portions of said outer wall surface of said tank.

4. An arrangement according to claim 2, wherein each keying device consists of a key-forming lug-like slide-block and a key-way forming clevis projecting radially towards each other in opposite directions from their respective attachments; each clevis defining a guiding path consisting of a substantially straight elongated slot forming a substantially vertical throughpassageway and extending from a closed end thereof near the attachment of said clevis to its opposite open end remote from said attachment, said slot being open both at its top and bottom and having opposite confronting edge side-faces located on either side of said relative vertical center plane of symmetry, said slideblock constantly engaging in sliding relationship said slot, thereby allowing relative reciprocal motion through thermal expansion and contraction between said slide-block and slot horizontally inwards and outwards as well as vertically upwards and downwards in either direction with two degrees of freedom of motion in substantially parallel relation to said vertical local center plane of symmetry. I

5. An arrangement according to claim 4, wherein each aforesaid clevis consists of a pair of spaced parallel arm-like portions the confronting sides of which form substantially symmetrical jaws defining said slotlike guiding path'therebetween whereas each aforesaid slide-block is formed with opposite parallel substantially flat faces slidably engaging said jaws.

6. An arrangement according to claim 5, wherein each one of said jaws carries a heat-insulating pad, said pads defining a plane bearing for said slide-block.

7. An arrangement according to claim 4, wherein at least one of said co-operating slide-block and clevis of each aforesaid keying device is provided with an antifriction lining.

8. An arrangement according to claim 4, wherein at least one of said co-operating slide-block and clevis of each aforesaid keying'device of at least one of said pluralities of keying devices is provided with a heatinsulating lining.

9. An arrangement according to claim 8, wherein said heat-insulating lining is interposed between the cooperating slide block and clevis of each aforesaid keying device of said external plurality of keying devices whereas said tank together with said tank-bound elements and said ring together with both of said ringbound elements and members are made from a metal capable of withstanding low temperatures.

10. An arrangement according to claim 4, wherein said weight-bearing means consist of several stationary brackets integral with and radially projecting inwards from said structure incircumferentially spaced relationship substantially on a level with each other, said ring freely resting on said brackets at least under normal rest conditions.

11. An arrangement according to claim 10, wherein at least some of said clevis are carried by said structure whereas said slide-blocks associated with said clevis are carried by said ring and at least some of said brackets are located below the slots of corresponding clevis, re spectively, and extend to have at least their free end portions located underneath said associated slideblocks which may thus rest thereupon for supporting said ring thereby.

12. An arrangement according to claim 1, wherein at least the outer wall surface of said tank has at least one axis of symmetry extending at right angles to both of said axes of swing.

13. An arrangement according to claim 12, wherein said ring is substantially symmetrical with respect to an axis extending in coaxial relation to that of said tank.

14. An arrangement according to claim 13, wherein at least the outer wall surface of said tank has the shape of a body of revolution about said axis of symmetry and said ring has also the shape of a body of revolution about said same axis of symmetry, so that said relative displacements of said tank and ring are allowed in respective meridian planes passing through said axis of revolution.

15. An arrangement according to claim 1, wherein said tank has a relative horizontal plane of symmetry parallel to both of said axes of swing and there are at least two sets of said keying means located at two levels substantially and overlying symmetrical relationship on either side of said horizontal plane of symmetry. I

16. An arrangement according to claim 15, including a substantially spheroidal tank mounted on a vehicle and in particular in the hold of a cargo ship having a main deck, said tank being movably suspended from the hull structure of said ship, the upper one of said sets of keying means being positioned substantially at the level of said main deck. 

1. In a construction including: a self-supporting structure undergoing roll and pitch rocking motions about two structurebound orthogonal geometrical axes of swing, respectively; a rigid tank supported mainly in weight-bearing relationship and at least partially encompassed by said structure; and an auxiliary device for bodily constraining said tank against roll and pitch with respect to said structure while allowing substantially free thermal expansion and contraction thereof; the improvement consisting in that said device comprises: at least one ring externally surrounding said tank and interposed in spaced relationship between the later and said structure; said ring being substantially parallel to the plane defined by the respective directions of said axes of swing; movably co-operating discrete keying means integral with said ring, structure and tank, respectively and providing slidable engagement of said ring with said structure and tank, respectively, to hold said ring against body motion parallel to said plane at least relative to said structure while allowing substantially free thermal expansion and contraction of said ring as well as substantially free body displacements thereof in parallel relation perpendicular to said plane; and weight-bearing means for unilaterally supporting said ring against its own weight while allowing its thermal expansion and contraction and body displacements therefrom.
 2. An arrangement according to claim 1, wherein said keying means comprise: at least one external plurality of discrete keying devices distributed about the outer periphery of said ring between the latter and said structure at least approximately on a same horizontal level and consisting each one of a pair of mating ring-bound and structure-bound members carried by saId ring and structure, respectively, and co-operating in slidable forced-guiding relationship, said ring-bound member defining one of a key and key-way whereas said structure-bound member defines the other of a key and key-way and engages said corresponding ring-bound member in slidable interfitting relationship; and at least one internal plurality of discrete keying devices distributed along the inner periphery of said ring and about the outer periphery of said tank between said ring and tank at least approximately on a same relative horizontal level and consisting each one of a pair of mating ring-bound and tank-bound elements carried by said ring and tank, respectively, and co-operating in slidable forced-guiding relationship, said ring-bound element defining one of a key and key-way whereas said tank-bound element defines the other of a key and key-way and engages said associated ring-bound element in slidable interfitting relationship, each keying device being at least approximately symmetrical with respect to a relative vertical center plane locally normal to the wall surface of said tank and perpendicular to said plane defined by said axes of swing; whereby the relative displacements of said ring and tank are confined to said relative vertical center planes.
 3. An arrangement according to claim 2, wherein the general configuration of the contour of said ring conforms in at least approximately parallel relationship to the local shape of at least the adjacent portion of the outer wall surface of said tank whereby the thermal deformations of said ring at least approximately follow those of said adjacent portions of said outer wall surface of said tank.
 4. An arrangement according to claim 2, wherein each keying device consists of a key-forming lug-like slide-block and a key-way forming clevis projecting radially towards each other in opposite directions from their respective attachments; each clevis defining a guiding path consisting of a substantially straight elongated slot forming a substantially vertical through-passageway and extending from a closed end thereof near the attachment of said clevis to its opposite open end remote from said attachment, said slot being open both at its top and bottom and having opposite confronting edge side faces located on either side of said relative vertical center plane of symmetry, said slide-block constantly engaging in sliding relationship said slot, thereby allowing relative reciprocal motion through thermal expansion and contraction between said slide-block and slot horizontally inwards and outwards as well as vertically upwards and downwards in either direction with two degrees of freedom of motion in substantially parallel relation to said vertical local center plane of symmetry.
 5. An arrangement according to claim 4, wherein each aforesaid clevis consists of a pair of spaced parallel arm-like portions the confronting sides of which form substantially symmetrical jaws defining said slot-like guiding path therebetween whereas each aforesaid slide-block is formed with opposite parallel substantially flat faces slidably engaging said jaws.
 6. An arrangement according to claim 5, wherein each one of said jaws carries a heat-insulating pad, said pads defining a plane bearing for said slide-block.
 7. An arrangement according to claim 4, wherein at least one of said co-operating slide-block and clevis of each aforesaid keying device is provided with an anti-friction lining.
 8. An arrangement according to claim 4, wherein at least one of said co-operating slide-block and clevis of each aforesaid keying device of at least one of said pluralities of keying devices is provided with a heat-insulating lining.
 9. An arrangement according to claim 8, wherein said heat-insulating lining is interposed between the co-operating slide block and clevis of each aforesaid keying device of said external plurality of keying devices whereas said tank together with said tank-bound elements and said ring together with both of said Ring-bound elements and members are made from a metal capable of withstanding low temperatures.
 10. An arrangement according to claim 4, wherein said weight-bearing means consist of several stationary brackets integral with and radially projecting inwards from said structure in circumferentially spaced relationship substantially on a level with each other, said ring freely resting on said brackets at least under normal rest conditions.
 11. An arrangement according to claim 10, wherein at least some of said clevis are carried by said structure whereas said slide-blocks associated with said clevis are carried by said ring and at least some of said brackets are located below the slots of corresponding clevis, respectively, and extend to have at least their free end portions located underneath said associated slide-blocks which may thus rest thereupon for supporting said ring thereby.
 12. An arrangement according to claim 1, wherein at least the outer wall surface of said tank has at least one axis of symmetry extending at right angles to both of said axes of swing.
 13. An arrangement according to claim 12, wherein said ring is substantially symmetrical with respect to an axis extending in coaxial relation to that of said tank.
 14. An arrangement according to claim 13, wherein at least the outer wall surface of said tank has the shape of a body of revolution about said axis of symmetry and said ring has also the shape of a body of revolution about said same axis of symmetry, so that said relative displacements of said tank and ring are allowed in respective meridian planes passing through said axis of revolution.
 15. An arrangement according to claim 1, wherein said tank has a relative horizontal plane of symmetry parallel to both of said axes of swing and there are at least two sets of said keying means located at two levels substantially and overlying symmetrical relationship on either side of said horizontal plane of symmetry.
 16. An arrangement according to claim 15, including a substantially spheroidal tank mounted on a vehicle and in particular in the hold of a cargo ship having a main deck, said tank being movably suspended from the hull structure of said ship, the upper one of said sets of keying means being positioned substantially at the level of said main deck. 